Abstract
Background. Osteoarthritis is the most common type of arthritis. It is the main cause of chronic musculoskeletal pain and disability, it decreases the flexibility of the joint, and causes pain, joint effusion and loss of function among the elderly population.
Objective. To examine how HILL therapy (High intensity laser therapy NDYAG 1064 nm) affects knee osteoarthritis. Design. A prospective randomized controlled trial. Setting. Outpatient Swiss physical therapy center.
Methods. Thirty patients of both gender having bilateral knees osteoarthritis were recruited and randomized into two equal groups: the control group received a program of selected quadriceps muscle sets exercise and hamstring, calf muscles stretching for 4 weeks, and the study group received the same control group interventions in addition to HILL application. Ultrasonography degree was the primary outcome, While Western Ontario and McMaster universities (WOMAC) osteoarthritis index measures were the secondary outcomes. All variables were measured at the baseline and after 4 weeks of the intervention.
Results. Statistical analysis was done by using paired’ test which showed significant improvement in both groups. Therefore, there was a significant difference between Group(A) and Group(B), showing that HILL group(A) is more effective than group(B) on pain, Stiffness, Function and ultrasonographic findings (p < 0.05).
Conclusion. Using HILT with a standard program of quadriceps muscle strengthen exercise sets and hamstring, calf muscles stretching has more beneficial effects on bilateral knee osteoarthritis than practicing the exercise program alone.

Keywords
knee osteoarthritis, high power laser, physical exercise, ultrasonography